North Korea’s artillery shelling near a South Korean warship patrolling disputed waters was likely a warning, not an attack attempt, Seoul officials and analysts said Friday.

On Thursday, the two Koreas exchanged artillery fire along the poorly marked western sea boundary. South Korean officials say the exchange started after two North Korean artillery shells fell in waters near a South Korean navy ship on a routine patrol of the area.

The South Korean ship wasn’t hit but fired several artillery rounds into waters near one of several North Korean warships near the sea boundary, South Korean defense officials said. The North Korean ship also wasn’t hit.

The North doesn’t recognize the Yellow Sea boundary, which was unilaterally drawn by the U.S.-led U.N. Command at the end of the 1950-53 Korean War.

Defense Ministry spokesman Kim Min-seok said Friday that South Korean officials suspect the North Korean shells came from a land-based artillery system, but they haven’t officially pinpointed the origin. Defense officials had said Thursday that the North’s shelling came from a warship.

Kim said officials believe North Korea didn’t aim to attack the South Korean navy ship because the North only fired two rounds. The North Korean ships in the area also didn’t leave the area after the North fired shells, something they would have done to avoid counter-fire if the North had intended to hit a South Korean ship, he said.

On Tuesday, South Korean navy ships fired warning shots to repel three North Korean warships that briefly violated the disputed sea boundary. On Wednesday, North Korea’s military vowed to retaliate.

Koh Yu-hwan, a professor at Seoul’s Dongguk University, said the North likely didn’t want to hit South Korean ships because Pyongyang doesn’t want fighting to divert public attention from widespread criticism of South Korean government incompetence in the handling of a ferry disaster last month that left more than 300 people dead or missing.

On Friday, North Korea’s military issued a statement denying it fired artillery shells. It claimed a South Korean warship intruded into North Korean waters and initiated firing on its own.

Kim, the South Korean spokesman, called the North Korean statement a “brazen lie.”

Thursday’s artillery exchange, which forced hundreds of residents on a frontline island to flee to bomb shelters, is the latest sign of rising animosity between the divided countries in recent weeks. North Korea has conducted a string of artillery drills and missile tests and threatened the leaders of the U.S. and South Korea.

In Washington, a State Department spokeswoman urged North Korea “to refrain from provocative actions” and to exercise restraint.

Both Koreas regularly conduct artillery drills in the disputed waters, which have been the scene of three bloody naval skirmishes between the rival Koreas since 1999.